ENZYMATIC PRODUCTION OF ALLULOSE

Abstract

The invention relates to improved processes for the enzymatic production of allulose using enzymes which have been characterized as having improved expression, improved stability, and low allulose to fructose conversion activity, relative to enzymes in other allulose production methods. Improved processes include steps of converting fructose-6-phosphate to allulose 6-phopsphate A6P) using an allulose 6-phosphate epimerase, and converting A6P to allulose using an allulose-6-phosphate phosphatase.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No. 63/026,294, filed on May 18, 2020, which is incorporated herein by reference in its entirety.

SEQUENCE LISTING

The Sequence Listing submitted herewith is an ASCII text file (2021-05-18_Sequence_Listing_ST25, created on May 18, 2021, 48,103 bytes) via EFS-Web is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to improved enzymatic processes for producing D-allulose.

BACKGROUND

D-allulose, which is also known as D-psicose, or simply, allulose, is a low-calorie, natural sweetener with 70% the sweetness of sucrose, but only 10% of its calories. It is a naturally occurring monosaccharide hexose, and is present in small amounts in wheat and other plants. Allulose was approved as a food additive by the Food and Drug Administration (FDA) in 2012, which designated it as generally recognized as safe (GRAS). However, allulose's high cost has limited its use as a sweetener. Nevertheless, in addition to having 10% of the calories of sucrose, Allulose boasts numerous health benefits, including a low glycemic index of 1; full absorbtion in the small intestine without being metabolized, resulting in its elimination in urine and feces; and inhibition of alpha-amylase, sucrase and maltase to help regulate blood sugar—all while having a functionality in foods and beverages that is similar to that of sucrose. As such, allulose has a variety of applications in the food and beverage industries.

Allulose is produced, predominantly, by methods involving enzymatic isomerization of fructose. See, for example, PCT Application Publication No. WO 2014/049373. Overall, such methods are not commercially viable because the costly separation of allulose from fructose, and relatively low product yields associated with them result in higher feedstock costs.

An alternative process for producing allulose by using an epimerase to catalyze fructose 6-phosphate to allulose 6-phosphate, followed by a dephosphorylation step is described in PCT Application Publication Nos. WO 2018/112139, WO 2018/004308, and WO 2018/129275, but these, and other alternative allulose production methods, do not satisfy a long-standing need for a process for producing allulose that provides a higher yield, using lower amounts of enzymes. With such improvements in mind, the following disclosure describes enzymes for use in the production of allulose, which have greater expression, stability, and are associated with low undesired allulose conversion activity, relative to currently employed allulose production methods. The foregoing improvements meet a strong industrial and commercial interest in decreasing the cost of allulose production.

SUMMARY OF THE INVENTION

The invention provides improved allulose preparation methods of enzymatically converting saccharides, such as, for example, polysaccharides, oligosaccharides, disaccharides, sucrose, D-glucose, and D-fructose into allulose. In one aspect, an improved process of the invention for the production of allulose from a saccharide includes a step of converting fructose-6-phosphate (F6P) to allulose 6-phopsphate (A6P), using an allulose 6-phosphate epimerase (A6PE), wherein the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1. In another aspect, an improved process according to the invention for the production of allulose from a saccharide includes a step of converting A6P to allulose, using an allulose-6-phosphate phosphatase (A6PP), wherein the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2. In an embodiment of the invention, the improved process includes a step of converting fructose-6-phosphate (F6P) to allulose 6-phopsphate (A6P), using an allulose 6-phosphate epimerase (A6PE), wherein the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and a step of converting A6P to allulose using a allulose-6-phosphate phosphatase (A6PP), wherein the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

A process of the invention for preparing allulose may also involve converting glucose 6-phosphate (G6P) to F6P, in a step catalyzed by phosphoglucoisomerase (PGI). Other processes according to the invention may further include a step of converting glucose 1-phosphate (G1P) to G6P by a reaction catalyzed by phosphoglucomutase (PGM), while still other processes may further include conversion of a saccharide to G1P by a reaction catalyzed by at least one other enzyme.

Saccharides used in any of the processes described herein can be selected from a group consisting of a starch or its derivative, cellulose or its derivative, and sucrose. In that regard, a starch or its derivative can be, for example, amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltose, maltotriose, or glucose. In some improved processes of the invention, starch is converted to a starch derivative by enzymatic hydrolysis or by acid hydrolysis of starch. Examples of enzymatic hydrolysis of starch to yield a starch derivative include, but are not limited to, reactions catalyzed by isoamylase, pullulanase, alpha-amylase, or a combination of two or more of these enzymes. Some processes of the invention can additionally involve adding 4-glucan transferase (4GT).

Other processes of the invention for preparing allulose further include a step of converting fructose to F6P, catalyzed by at least one enzyme. Other processes of the invention further include a step of converting sucrose to the fructose, in a reaction catalyzed by at least one enzyme. G6P, which is used in processes for preparing allulose can also be generated by converting glucose to the G6P, in a reaction catalyzed by at least one enzyme. Glucose can, in turn, be produced by converting sucrose to glucose, catalyzed by at least one enzyme.

Processes of the invention can be conducted under various reaction conditions, including at a temperature ranging from about 37° C. to about 85° C., at a pH ranging from about 4 to about 9, and/or for about 0.5 hour to about 48 hours, or as continuous reactions. In some embodiments, the steps of a process for preparing allulose are conducted under any one or more of the foregoing reaction conditions in a single reactor. While, in other embodiments, reaction steps are conducted under the foregoing reaction conditions using a plurality of bioreactors, which may be arranged in a series.

In some processes of the invention, the steps for preparing allulose are conducted under conditions that do not contain adenosine triphosphate (ATP) or NAD(H), i.e., ATP-free or NAD(H)-free, at a phosphate concentration from about 0.1 mM to about 150 mM, the phosphate is recycled, and/or the step of converting A6P to allulose involves an energetically favorable chemical reaction.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram illustrating an enzymatic pathway converting starch or its derived products to allulose. The following abbreviations are used: αGP, alpha-glucan phosphorylase or starch phosphorylase; PGM, phosphoglucomutase; PGI, phosphoglucoisomerase; A6PE, allulose 6-phosphate epimerase; A6PP, allulose 6-phosphate phosphatase; IA, isoamylase; PA, pullulanase; MP, maltose phosphorylase; PPGK, polyphosphate glucokinase. In processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

FIG. 2 shows an enzymatic pathway converting cellulose or its derived products to allulose. CDP, cellodextrin phosphorylase; CBP, cellobiose phosphorylase; PPGK, polyphosphate glucokinase; PGM, phosphoglucomutase; PGI, phosphoglucoisomerase; A6PE, allulose 6-phosphate epimerase; A6PP, allulose 6-phosphate phosphatase. In processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

FIG. 3 is a schematic diagram illustrating an enzymatic pathway converting fructose to allulose. PPFK, polyphosphate fructokinase; A6PE, allulose 6-phosphate epimerase; A6PP, allulose 6-phosphate phosphatase. In processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

FIG. 4 is a schematic diagram illustrating an enzymatic pathway converting glucose to allulose. PPGK, polyphosphate glucokinase; PGI, phosphoglucoisomerase; A6PE, allulose 6-phosphate epimerase; A6PP, allulose 6-phosphate phosphatase. In processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

FIG. 5 shows an enzymatic pathway converting sucrose or its derived products to allulose. SP, sucrose phosphorylase; PPFK, polyphosphate fructokinase; PGM, phosphoglucomutase; PGI, phosphoglucoisomerase; A6PE, allulose 6-phosphate epimerase; A6PP, allulose 6-phosphate phosphatase. In processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

FIG. 6 shows the conversion of maltodextrin to allulose measured by HPLC. The following enzymes were used: αGP (Uniprot ID G8NCC0), PGM (Uniprot ID A0A150LLZ1), PGI (Uniprot ID Q5SLL6), A6PP (Uniprot ID A0A0E3NCH4), and 4GT (Uniprot ID E8MXP8). A6PEs (Uniprot IDs A0A090IXZ8) and (Uniparc ID UPI000411882A) were compared with an A6PE used in the improved processes of the invention (A0A223HZI7).

FIG. 7 shows the conversion of G1P to allulose measured by HPLC. The following enzymes were used: PGM (Uniprot ID A0A150LLZ1), PGI (Uniprot ID Q5SLL6), and A6PE (Uniprot ID D9TQJ4). A6PP (Uniprot ID A3DC21) was compared with an A6PP used in the improved processes of the invention, (Uniprot ID A0A0E3NCH4).

DETAILED DESCRIPTION

The invention described here relates to improved enzymatic processes for converting saccharides to allulose. More particularly, the invention relates to improved cell-free, enzymatic processes for the conversion of saccharides to allulose. Examples of saccharides, which may be converted to allulose by a process of the invention include, but are not limited to, starch, cellulose, sucrose, glucose, fructose, and products derived from any the foregoing saccharides. Enzymes used in a process according to the invention may be combined into a single cell-free enzyme cocktail. Indeed, in comparison to cell-based manufacturing methods for producing allulose, a process according provides higher reaction rates due, at least in part, to the absence of cell membranes, which can slow down the transport of substrate, product, or both, into and out of the cells used in the process. Processes of the invention also yield a final allulose product that is free of nutrient-rich metabolites associated with fermentation media and cells used in cell-based processes.

Some processes of the invention for producing allulose improve the step of converting fructose-6-phosphate (F6P) to allulose 6-phosphate (A6P) by a reaction catalyzed by an allulose 6-phosphate epimerase (A6PE), which has one or more improved properties relative to any one of the A6PE enzymes used in allulose production methods prior to the invention. Other processes of the invention improve the step of converting A6P to allulose by a reaction catalyzed by an allulose-6-phosphate phosphatase (A6PP), which has one or more improved properties relative to any one of the A6PP enzymes used in allulose production methods prior to the invention. In some processes of the invention, the process for producing allulose may include (F6P to A6P) and (A6P to allulose) conversion steps in which an improved A6PE and an improved A6PP are used for the (F6P to A6P) and (A6P to allulose) conversion steps, respectively. Other processes of the invention for producing allulose may use an improved A6PE for the F6P to A6P conversion step, while using an unimproved A6PP for the A6P to allulose conversion step. Conversely, there are also processes of the invention that use an unimproved A6PE for the F6P to A6P conversion step, and an improved A6PP for the A6P to allulose conversion step. See PCT Publication WO2018/112139, which is herein incorporated by reference in its entirely, for examples of A6PEs and A6PPs, including A6PE from Thermoanaerobacterium thermosaccharolyticum (UniProt ID D9TQJ4), A6PE from Bacillus thermoamylovorans (UniProt ID A0A090IXZ8), and A6PP from Clostridium thermocellum (UniProt ID A3DC21).

Using enzymes with higher activities and more favorable properties, such as improved stability, in a process for producing allulose allows for using lower amounts of enzymes, thereby reducing the cost of the overall process. As discussed above, the conversion of F6P to A6P in an improved process of the invention is catalyzed by an A6PE with improved properties, which contribute to improvements in an allulose production process, including one or more of the following improved properties: a higher expression yield, thermostability, and low undesired allulose to fructose epimerization activity, which is also referred to as fructose reversion, in comparison to the thermophilic A6PE from Thermoanaerobacterium thermosaccharolyticum (UniProt ID D9TQJ4).

In some processes of the invention, the expression yield of an A6PE in an improved process has an expression yield, which is at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 100%, at least 200%, at least 300% or at least 400% higher than the expression yield of an A6PE in an unimproved process such as, but not limited to, an A6PE with an amino acid sequence of UniProt ID D9TQJ4 (Thermoanaerobacterium thermosaccharolyticum). For example, in a process the invention for producing allulose, the step of converting F6P to A6P uses an A6PE with an amino acid sequence of UniProt ID A0A223HZI7 (Clostridium thermosaccharolyticum) with an expression yield, which is approximately 300%, 310%, 320%, 330%, 340%, 350%, 360%, 370%, 380%, 390%, or 400% higher than an A6PE with an amino acid sequence of UniProt ID D9TQJ4.

In some processes of the invention, an A6PE in an improved process is more stable than an A6PE in an unimproved process. More particularly, an A6PE in an improved process of the invention may be more thermostable than A6PE in an unimproved process. Indeed, the A6PE in some processes of the invention may remain 50%-60% soluble, 60%-70% soluble, 70%-80% soluble, 80%-90% soluble, 90%-100% soluble, or 100% soluble, after 30 minutes at 50° C.-60° C. In a process of the invention in which the conversion of F6P to A6P uses an A6PE in an improved process with an amino acid sequence of UniProt ID A0A223HZI7, the A6PE may remain about 80% soluble after 30 minutes at about 60° C.; therefore, the A6PE in an improved process may be at least 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85% soluble after 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 minutes at 54° C., 55° C., 56° C., 57° C., 58° C., 59° C., 60° C., 61° C., 62° C., 63° C., 64° C., 65° C., or 66° C.

The conversion of allulose to fructose by A6PE in a process for producing allulose is undesirable. In some improved processes of the invention, A6PE-dependent allulose to fructose conversion activity is lower than it is in unimproved processes for producing allulose. In an improved process of the invention, for example, no more than 1%, no more than 0.9%, no more than 0.8%, no more than 0.7%, no more than 0.6%, no more than 0.5%, no more than 0.4%, no more than 0.3%, no more than 0.2%, no more than 0.1%, or 0% of allulose produced by a process of the invention is converted to fructose.

A6PE enzymes used in improved processes of the invention are specific for F6P/A6P, and the epimerization catalyzed by the A6PE is reversible. The term “specific”, as used here, means the F6/A6P epimerization activity of an A6PE in an improved process of the invention is higher than it is for other phosphorylated monosaccharides present in the reaction. For example, the F6P/A6P epimerization activity of the A6PE in an improved process of the invention is higher than its epimerization activity for G6P.

The F6P to A6P conversion in improved processes of the invention may utilize a divalent metal A6PE cofactor, such as magnesium, manganese, cobalt, or zinc. In some processes of the invention, for example, cobalt is a cofactor of A6PE in the F6P to A6P conversion reaction step.

As discussed above, examples of properties of A6PE enzymes in improved processes of the invention include, but are not limited to, increased expression yield, increased stability, and decreased conversion of allulose to fructose. In some improved processes of the invention, the amino acid sequence of the A6PE thermophilic. More particularly, the A6PE in certain improved processes of the invention has an amino acid sequence, which shares 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 99%, or 100% sequence identity with an A6PE from Clostridium thermosaccharolyticum. Accordingly, in some improved processes of the invention, the amino acid sequence of the A6PE shares 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 99%, or 100% sequence identity with the amino acid sequence of the C. thermosaccharolyticum thermophilic epimerase with the sequence of UniPRot ID A0A223HZI7.

Another structural feature of A6PE in some improved processes of the invention is an (α/β)8-barrel domain for catalysis. In some of those improved processes of the invention, the (α/β)8-barrel domain contains a phosphate binding domain with a Ser at the end of the 7^th β strand of the barrel, a Ser at the end of the 8^th β-strand of the barrel, and a Gly in the active site loop. In other improved processes of the invention, the A6PE contains a metal binding domain with a His in the 2^nd and 3^rd β-strands of the barrel. In other improved processes of the invention, the A6PE contains an Asp in the 2^nd and 7^th β-strand of the barrel to act as the acid/base catalyst for 1,1 proton transfer. In other improved processes of the invention, the A6PE contains a His hydrophobic residue-Asp signature in the 2^nd β-strand of the barrel where the His is utilized in metal binding and the Asp for acid/base catalysis. In other improved processes of the invention, the A6PE is a member of the Ribulose-phosphate 3 epimerase family (Pfam PF00834). In yet other improved processes of the invention, the A6PE contains two or more of any of the (α/β)8-barrel domain structural features described above. Accordingly, in some improved processes of the invention, the A6PE contains an (α/β)8-barrel domain for catalysis, a Ser at the end of the 7th β-strand of the barrel, a Ser at the end of the 8^th β strand of the barrel, a Gly in the active site loop, a His in the 2^nd and 3^rd β-strands of the barrel, an Asp in the 2nd and 7th β-strand of the barrel, a His-hydrophobic residue-Asp signature in the 2nd β-strand of the barrel, and is a member of the Ribulose-phosphate 3 epimerase family (Pfam PF00834) These features of (α/β)8-barrel domains are known in the art, and are referenced in, for example, Chan et al. Structural Basis for Substrate Specificity in Phosphate Binding (beta/alpha)8-Barrels: D-Allulose 6-Phosphate 3-Epimerase from Escherichia coli K-12. Biochemistry 2008; 47(36):9608-9617.

In an improved processes of the invention, allulose-6-phosphate phosphatase (A6PP) is a phosphatase that specifically converts A6P to allulose. Thus, an A6PP in an improved processes of the invention is specific for A6P. The term “specific”, as used here, means the A6P dephosphorylation activity of A6PP is higher than it is for other phosphorylated monosaccharides in the process. For example, an A6PP of the improved process of the invention has a higher dephosphorylation activity on A6P than on G1P, G6P, and F6P. The A6PP in an improved process of the invention may also utilize a divalent metal cofactor, such as zinc, manganese, cobalt, or magnesium, preferably magnesium.

The conversion of A6P to allulose in an improved process of the invention may use an A6PP with increased activity relative to any of the A6PP enzymes used in processes for producing allulose prior to the invention. In some improved processes of the invention, for example, A6PP converts A6P to allulose with a higher activity than A6PP from Clostridium thermocellum (UniProt ID A3DC21). See International Patent Application Publications WO 2018/112139 and WO 2018/129275, which are herein incorporated by reference in their entireties. More particularly, in an improved process of the invention, the A6PP has an amino acid sequence of an A6PP from Methanosarcina thermophila CHTI-55, with A6P to allulose activity, which is improved by at least 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, or 300% relative to the activity of the A6PP from Clostridium thermocellum with an amino acid sequence of UNIPROT ID A3DC21. Even more particularly, in some improved processes of the invention, the A6PP has an amino acid sequence of Uniprot ID A0A0E3NCH4 (SEQ ID NO. 2) with A6P to allulose activity, which is improved by at least 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, or 300% relative to the activity of the A6PP from Clostridium thermocellum with an amino acid sequence of UNIPROT ID A3DC21.

In some improved processes of the invention, the A6PP has an amino acid sequence, which shares 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 99%, or 100% sequence identity with an A6PP from Methanosarcina thermophila CHTI-55. Accordingly, in some improved processes of the invention, the amino acid sequence of the A6PP shares 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 99%, or 100% sequence identity with the amino acid sequence of the Methanosarcina thermophila CHTI-55 phosphatase with the sequence of UniProt ID A0A0E3NCH4 (SEQ ID NO. 2).

Another structural feature of A6PE in some improved processes of the invention is a Rossmanoid fold domain for catalysis. In some of those improved processes of the invention, the A6PP contains one or more of the following features: a C1 capping domain for substrate specificity; a D×D signature in the 1^st β-strand of the Rossmanoid fold for coordinating magnesium, where the second Asp is a general acid/base catalyst; a Thr or Ser at the end of the 2^nd β-strand of the Rossmanoid fold that helps stability of reaction intermediates; a Lys at the N-terminus of the α-helix C-terminal to the 3^rd β-strand of the Rossmanoid fold that helps stability of reaction intermediates; and a E(D/N) signature at the end of the 4^th β-strand of the Rossmanoid fold for coordinating divalent metal cations, such as magnesium. See e.g., Burroughs et al., Evolutionary Genomics of the HAD Superfamily: Understanding the Structural Adaptations and Catalytic Diversity in a Superfamily of Phosphoesterases and Allied Enzymes. J. Mol. Biol. 2006; 361; 1003-1034. As established herein, an improved process of the invention includes a step of converting F6P to A6P, using an A6PE, and a step of converting A6P to allulose, using an A6PP. An improved process of the invention may also include additional upstream steps. For example, some processes of the invention produce allulose from a saccharide using phosphoglucose isomerase (PGI) to convert glucose 6-phosphate (G6P) to F6P. Exemplary PGIs which may be used include those disclosed in International Patent Application Publication WO2017/059278: PGI from Clostridium thermocellum (Uniprot ID A3DBX9) and PGI from Thermus thermophilus (Uniprot ID Q5SLL6).

Some improved processes of the invention also include a step of converting glucose 1-phosphate (G1P) to G6P using phosphoglucomutase (PGM). An example of a PGM is PGM from Thermococcus kodakaraensis (Uniprot ID Q68BJ6), disclosed in International Patent Application Publication WO2017/059278; or PGM from Caldibacillus debilis (Uniprot A0A150LLZ1), disclosed in PCT Application Publication 2020/092315.

Some improved processes of the invention also include a step of converting a saccharide to the G1P, using at least one enzyme. For example, an improved process may convert a saccharide selected from a starch or derivative thereof, as described in FIG. 1, cellulose or a derivative thereof, as described in FIG. 2, fructose, as described in FIG. 3, glucose, as described in FIG. 4, or sucrose, as described in FIG. 5. The enzyme or enzymes used in the step of converting a saccharide to the G1P in such improved processes of the invention may be, for example, alpha-glucan phosphorylase (αGP), maltose phosphorylase, sucrose phosphorylase, cellodextrin phosphorylase, cellobiose phosphorylase, and/or cellulose phosphorylase, and mixtures thereof. The choice of the enzyme or enzyme combination to arrive at F6P depends on the saccharide used in the process.

Cellulose is the most abundant bioresource and is the primary component of plant cell walls. Non-food lignocellulosic biomass contains cellulose, hemicellulose, and lignin as well as other minor components. Pure cellulose, including Avicel (microcrystalline cellulose), regenerated amorphous cellulose, bacterial cellulose, filter paper, and so on, can be prepared via a series of treatments. The partially hydrolyzed cellulosic substrates include water-insoluble cellodextrins whose degree of polymerization is more than 7, water-soluble cellodextrins with degree of polymerization of 3-6, cellobiose, glucose, and fructose.

In some improved processes of the invention, cellulose and its derived products may be converted to allulose by a series of enzymatic steps, including: generating G1P from cellodextrin and cellobiose and free phosphate catalyzed by cellodextrin phosphorylase (CDP) and cellobiose phosphorylase (CBP), respectively; converting G1P to G6P catalyzed by PGM; converting G6P to F6P catalyzed by PGI; converting F6P to allulose as described above, and the phosphate ions can be recycled by the step of converting cellodextrin and cellobiose to G1P.

Several enzymes may be used to hydrolyze solid cellulose to water-soluble cellodextrins and cellobiose. Such enzymes include endoglucanase and cellobiohydrolase, but not including beta-glucosidase (cellobiase). Prior to cellulose hydrolysis and G1P generation, cellulose and biomass can be pretreated to increase their reactivity and decrease the degree of polymerization of cellulose chains. Cellulose and biomass pretreatment methods include dilute acid pretreatment, cellulose solvent-based lignocellulose fractionation, ammonia fiber expansion, ammonia aqueous soaking, ionic liquid treatment, and partial hydrolysis by using concentrated acids, including hydrochloric acid, sulfuric acid, phosphoric acid and their combinations.

When the saccharides include cellobiose, and the enzymes contain cellobiose phosphorylase, G1P is generated from cellobiose and phosphate by cellobiose phosphorylase. When the saccharides contain cellodextrins and the enzymes include cellodextrin phosphorylase, G1P is generated from cellodextrins and phosphate by cellodextrin phosphorylase. When the saccharides include cellulose, and enzymes contain cellulose phosphorylase, the G1P is generated from cellulose and phosphate by cellulose phosphorylase.

When the saccharides include maltose and the enzymes contain maltose phosphorylase, the G1P is generated from maltose and phosphate by maltose phosphorylase. If the saccharides include sucrose, and enzymes contain sucrose phosphorylase, the G1P is generated from sucrose and phosphate by sucrose phosphorylase.

When the saccharide is starch or a starch derivative, the derivative may be selected from the group consisting of amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltose, maltotriose, and glucose, and mixtures thereof. In certain processes of the invention, the enzymes used to convert a saccharide to G1P contain αGP. In this step, when the saccharides include starch, the G1P is generated from starch and phosphate by αGP; when the saccharides contain soluble starch, amylodextrin, or maltodextrin, the G1P is produced from soluble starch and phosphate, amylodextrin and phosphate, or maltodextrin and phosphate by αGP. An example of αGP is αGP from Thermotoga maritima (Uniprot ID G4FEH8), disclosed in International Patent Application Publication WO2017/059278; or αGP from Thermus sp. CCB_US3_UF1 (Uniprot G8NCC0), disclosed in International Patent Application Publication 2020/092315.

Some processes according to the invention may further comprise the step of converting starch to a starch derivative, where the starch derivative is prepared by enzymatic hydrolysis of starch or by acid hydrolysis of starch. In certain processes of the invention, maltose phosphorylase (MP) can be used to increase allulose yields by phosphorolytically cleaving the degradation product maltose into G1P and glucose. Alternatively, 4-glucan transferase (4GT) can be used to increase allulose yields by recycling the degradation products glucose, maltose, and maltotriose into longer maltooligosaccharides; which can be phosphorolytically cleaved by αGP to yield G1P. An example of 4GT is 4GT from Thermococcus litoralis (Uniprot ID 032462), disclosed in International Patent Application Publication WO2017/059278; or 4GT from Anaerolinea thermophila strain DSM 14523 (Uniprot E8MXP8), disclosed in International Patent Application Publication 2020/092315. In some processes of the invention, polyphosphate and polyphosphate glucokinase (PPGK) can be added to the process, thus increasing yields of allulose by phosphorylating the degradation product glucose to G6P.

Starch is the most widely used energy storage compound in nature and is mostly stored in plant seeds. Natural starch contains linear amylose and branched amylopectin. Examples of starch derivatives include amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltose, fructose, and glucose. Examples of cellulose derivatives include pretreated biomass, regenerated amorphous cellulose, cellodextrin, cellobiose, fructose, and glucose. Sucrose derivatives include fructose and glucose.

Where the processes use a starch derivative, the starch derivative can be prepared by enzymatic hydrolysis of starch catalyzed by isoamylase, pullulanase, α-amylase, or their combination. Corn starch contains many branches that impede αGP action. Isoamylase and pullulanase can be used to de-branch starch, yielding linear amylodextrin. Isoamylase-pretreated and pullulanase-pretreated starch can result in a higher F6P concentrations in the final product. Isoamylase and pullulanase cleave alpha-1,6-glycosidic bonds, which allows for more complete degradation of starch by alpha-glucan phosphorylase. Alpha-amylase cleaves alpha-1,4-glycosidic bonds, therefore alpha-amylase is used to degrade starch into fragments for quicker conversion to allulose.

Allulose can also be produced from fructose. See FIG. 3. Processes according to the inventions can also comprise the step of converting fructose to F6P, wherein the step is catalyzed by at least one enzyme and, optionally, the step of converting sucrose to the fructose, wherein the step is catalyzed by at least one enzyme. For example, the process involves generating F6P from fructose and polyphosphate catalyzed by polyphosphate fructokinase (PPFK). The conversion of F6P to allulose is described above. The fructose can be produced, for example, by an enzymatic conversion of sucrose. The phosphate ions generated when A6P is converted to allulose can then be recycled in the steps of converting sucrose to G1P.

Allulose can also be produced from glucose. See FIG. 4. Processes according to the inventions can also comprise the step of converting glucose to G6P, catalyzed by at least one enzyme, and, optionally, the step of converting sucrose to the fructose, wherein the step is catalyzed by at least one enzyme. For example, the process involves generating G6P from glucose and polyphosphate catalyzed by polyphosphate glucokinase (PPGK). The glucose can be produced, for example, by 4-glucan transferase recycling of maltotriose to longer chain maltodextrins.

In some methods of the invention, the phosphate ions generated when A6P is converted to allulose are recycled in the step of converting starch derivatives to G1P (See, e.g., FIG. 1), cellulose derivatives to G1P (See e.g., FIG. 2), or sucrose to G1P (See FIG. 5), especially if the process is conducted in a single reaction vessel. Additionally, PPFK and polyphosphate can be used to increase allulose yields by producing F6P from fructose generated by the phosphorolytic cleavage of sucrose by SP.

Processes for preparing allulose from a saccharide, for example, include the following steps: (i) converting a saccharide to glucose 1-phosphate (G1P) using one or more enzymes; (ii) converting G1P to G6P using phosphoglucomutase (PGM, EC 5.4.2.2); (iii) converting G6P to F6P using phosphoglucoisomerase (PGI, EC 5.3.1.9); (iv) converting F6P to A6P via allulose 6-phosphate epimerase (A6PE), and (v) converting A6P to allulose via allulose 6-phosphate phosphatase (A6PP). In improved processes of the invention, the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2. In such processes, for example, the enzyme in step (i) is αGP. Typically, the ratios of enzyme units used in the process are 1:1:1:1:1 (αGP:PGM:PGI:A6PE:A6PP). An enzyme unit is the amount of enzyme needed to convert 1 umol of substrate to product in 1 minute. Accordingly, an enzyme with a higher activity will have a lower amount of enzyme, in terms of mg of enzyme per one enzyme unit, compared to an enzyme with a lower activity which catalyzes the same reaction. To optimize product yields, these ratios can be adjusted in any number of combinations. For example, a particular enzyme may be present in an amount about 2×, 3×, 4×, 5×, etc. relative to the amount of other enzymes.

A process for preparing allulose according to the invention may include the following additional steps: generating glucose from polysaccharides and oligosaccharides by enzymatic hydrolysis or acid hydrolysis, converting glucose to G6P catalyzed by at least one enzyme, generating fructose from polysaccharides and oligosaccharides by enzymatic hydrolysis or acid hydrolysis, and converting fructose to G6P catalyzed by at least one enzyme. Examples of the polysaccharides and oligosaccharides are enumerated above.

Processes to prepare allulose according the invention can be conducted in a single bioreactor or reaction vessel. Alternatively, the steps can also be conducted in a plurality of bioreactors, or reaction vessels, that are arranged in series. In a preferred process, the enzymatic production of allulose is conducted in a single reaction vessel.

The enzymes used in the invention may take the form of soluble, immobilized, assembled, or aggregated proteins. These enzymes could be adsorbed on insoluble organic or inorganic supports commonly used to improve functionality, as known in the art. These include polymeric supports such as agarose, methacrylate, polystyrene, phenol-formaldehyde, or dextran, as well as inorganic supports such as glass, metal, or carbon-based materials. These materials are often produced with large surface-to-volume ratios and specialized surfaces that promote attachment and activity of immobilized enzymes. The enzymes might be affixed to these solid supports through covalent, ionic, or hydrophobic interactions. The enzymes could also be affixed through genetically engineered interactions such as covalent fusion to another protein or peptide sequence with affinity to the solid support, most often a poly-histidine sequence. The enzymes might be affixed either directly to the surface or surface coating, or they might be affixed to other proteins already present on the surface or surface coating. The enzymes can be immobilized all on one carrier, on individual carriers, or a combination of the two (e.g., two enzyme per carrier then mix those carriers). These variations can be mixed evenly or in defined layers to optimize turnover in a continuous reactor. For example, the beginning of the reactor may have a layer of αGP to ensure a high initial G1P increase. Enzymes may be immobilized all on one carrier, on individual carriers, or in groups. These enzymes may be mixed evenly or in defined layers or zones to optimize turnover.

Any suitable biological buffer known in the art can be used in an improved process of the invention, such as HEPES, PBS, BIS-TRIS, MOPS, DIPSO, Trizma, phosphate buffer, etc. The reaction buffer for all embodiments can have a pH ranging from 4.0-9.0. More preferably, the reaction buffer pH can range from about 6.0 to about 7.8. For example, the reaction buffer pH can be 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, or 7.8.

In some improved processes of the invention the reaction buffer contains divalent metal cations. Examples include Mn²⁺, Co²⁺, Mg²⁺ and Zn²⁺, and the like, preferably Co²⁺ and Mg²⁺. The concentration of divalent metal cations can range from about 0 mM to about 150 mM, from about 0 mM to about 100 mM, from about 1 mM to about 50 mM, preferably from about 5 mM to about 50 mM, or more preferably from about 10 mM to about 50 mM. For instance, the divalent metal cation concentration can be about 0.1 mM, about 0.5 mM, about 1 mM, about 1.5 mM, about 2 mM, about 2.5 mM, about 5 mM, about 6 mM, about 7 mM, about 8 mM, about 9 mM, about 10 mM, about 15 mM, about 20 mM, about 25 mM, about 30 mM, about 35 mM, about 40 mM, about 45 mM, about 50 mM, or about 55 mM.

The reaction temperature at which improved process steps are conducted can range from 37-85° C. More preferably, the steps are conducted at a temperature ranging from about 37° C. to about 85° C. The temperature can be, for example, about 40° C., about 45° C., about 50° C., about 55° C., or about 60° C. Preferably, the reaction temperature is about 50° C. In some improved processes of the invention, the reaction temperature is constant, and is not changed during the process.

The reaction time of the disclosed processes can be adjusted as necessary and can range from about 0.5 hour to about 48 hours. For example, the reaction time can be about 16 hours, about 18 hours, about 20 hours, about 22 hours, about 24 hours, about 26 hours, about 28 hours, about 30 hours, about 32 hours, about 34 hours, about 36 hours, about 38 hours, about 40 hours, about 42 hours, about 44 hours, about 46 hours, or about 48 hours. More preferably, the reaction time is about 24 hours.

The steps in an improved process of the invention may run in batch or in a continuous process using a packed bed reactor or similar device. In a continuous process, a solution maltodextrin would be pumped through a bed of immobilized enzyme at such a rate that conversion to allulose would be complete when the solution leaves the column for downstream processing. For example, 200 g/L of maltodextrin can be pumped through a column packed with immobilized enzymes (maintained at, for example, 50° C.) such that when the maltodextrin leaves the column maximum allulose yield is achieved. This methodology offers greater volumetric productivity over batch methods. This limits the time our product is in contact with the column and reaction conditions, which decreases chances of product degradation (e.g., potential hydroxymethylfurfural formation). Whether in batch or continuous mode the various steps of processes of the invention may be conducted using the same reaction conditions as the other steps. For example, in a particular process of the invention using a single bioreactor or reaction vessel, the reaction conditions such as pH and temperature, and reaction buffer are kept constant for all steps of the process.

Phosphate ions produced by A6PP dephosphorylation of A6P can then be recycled in the process step of converting a saccharide to G1P, particularly when all process steps are conducted in a single bioreactor or reaction vessel. The ability to recycle phosphate in the disclosed processes allows for non-stoichiometric amounts of phosphate to be used, which keeps reaction phosphate concentrations low. This affects the overall pathway and the overall rate of the processes, but does not limit the activity of the individual enzymes and allows for overall efficiency of the allulose making processes.

For example, reaction phosphate concentrations can range from about 0.1 mM to about 300 mM, from about 0.1 mM to about 150 mM, from about 1 mM to about 50 mM, preferably from about 5 mM to about 50 mM, or more preferably from about 10 mM to about 50 mM. For instance, the reaction phosphate concentration can be about 0.1 mM, about 0.5 mM, about 1 mM, about 1.5 mM, about 2 mM, about 2.5 mM, about 5 mM, about 6 mM, about 7 mM, about 8 mM, about 9 mM, about 10 mM, about 15 mM, about 20 mM, about 25 mM, about 30 mM, about 35 mM, about 40 mM, about 45 mM, about 50 mM, or about 55 mM.

Therefore, low phosphate concentrations result in decreased production costs due to low total phosphate and thus lowered cost of phosphate removal. It also prevents inhibition of A6PP by high concentrations of free phosphate and decreases the potential for phosphate pollution.

Furthermore, the processes disclosed herein can be conducted without added ATP as a source of phosphate, i.e., ATP-free. The processes can also be conducted without having to add NAD(H), i.e., NAD(H)-free. Other advantages also include the fact that at least one step of the disclosed processes for making allulose involves an energetically favorable chemical reaction. While the use of enzymes with higher activities will not affect the overall energetics, the ability to use lower amounts of enzymes in the improved processes is advantageous. The advantage is the reduction of the overall cost of enzyme in the total production cost of the product.

The processes according to the invention can achieve high yields due to the very favorable equilibrium constant for the overall reaction. Theoretically, up to 99% yields can be achieved if the starting material is completely converted to an intermediate. Also, the step of converting A6P to allulose according to the invention is an irreversible phosphatase reaction, regardless of the feedstock. Therefore, allulose is produced with a very high yield.

Processes of the invention use low-cost starting materials and reduce production costs by decreasing costs associated with the feedstock and product separation. Starch and its derivatives, cellulose and its derivatives, and sucrose are less expensive feedstocks than, for example, crystalline fructose. When allulose is produced from fructose, the yield is only ˜28% (WO 2016/160573). Fructose and allulose are then separated via chromatography, which together leads to higher production costs than the disclosed method.

Processes according to the invention allow for easy recovery of allulose, and separation costs are minimized. Preferably, in processes of the invention, the recovery of allulose is not via chromatographic separation. Following production of allulose in a continuous reaction, the product is instead passed through ultrafiltration, ion exchange (cation then anion, not mixed bed), concentration, crystallization, crystal isolation, and drying. Due to high yields of allulose, the crystallization step is all that is needed to purify allulose. To further purify allulose prior to crystallization, one can employ ultrafiltration to eliminate the risk of enzyme being present in the crystallization process or nanofiltration to remove any unconverted dextrins that may co-crystallize with allulose or limit the recyclability of the mother liquor (maltodextrin, maltotetraose, maltotriose, maltose, etc.).

An improved process for preparing allulose according to the invention includes the following steps: (i) converting a saccharide to glucose 1-phosphate (G1P) using one or more enzymes; (ii) converting G1P to G6P using phosphoglucomutase (PGM, EC 5.4.2.2); (iii) converting G6P to F6P using phosphoglucoisomerase (PGI, EC 5.3.1.9); (iv) converting F6P to A6P via allulose 6-phosphate epimerase (A6PE), and (v) converting A6P to allulose via allulose 6-phosphate phosphatase (A6PP), where the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or where the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2. This process is preferably conducted in a single bioreactor or reaction vessel.

Preferably, an improved process for preparing allulose according to the invention includes the following steps: (i) converting a saccharide to glucose 1-phosphate (G1P) using αGP, where the saccharide is selected from the group consisting of starch, one or more derivatives of starch, or a combination thereof; (ii) converting G1P to G6P using phosphoglucomutase (PGM, EC 5.4.2.2); (iii) converting G6P to F6P using phosphoglucoisomerase (PGI, EC 5.3.1.9); (iv) converting F6P to A6P via allulose 6-phosphate epimerase (A6PE), and (v) converting A6P to allulose via allulose 6-phosphate phosphatase (A6PP), where the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1, and/or where the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2. The process is preferably conducted in a single reactor vessel and may incorporate one or more of the various process conditions discussed above.

EXAMPLES

Materials and Methods All chemicals, including glucose 1-phosphate, magnesium chloride, sodium phosphate (mono and dibasic), are reagent grade or higher and purchased from Sigma-Aldrich (St. Louis, Mo., USA) or Fisher Scientific (Pittsburgh, Pa., USA), unless otherwise noted. E. coli BL21 (DE3) (Sigma-Aldrich, St. Louis, Mo., USA) was used as a host cell for recombinant protein expression. ZYM-5052 media containing 50 mg L−1 kanamycin was used for E. coli cell growth and recombinant protein expression.

Production and purification of recombinant enzymes The E. coli BL21 (DE3) strain harboring a protein expression plasmid (pET28a) was incubated in a 1 L Erlenmeyer flask with 100 mL of ZYM-5052 media containing 50 mg L⁻¹ kanamycin. Cells were grown at 37° C. with rotary shaking at 220 rpm for 16-24 hours. The cells were harvested by centrifugation at 12° C. and washed once with either: 20 mM HEPES (pH 7.5) containing 50 mM NaCl and 5 mM MgCl₂ for heat precipitation; or 20 mM HEPES (pH 7.5) containing 300 mM NaCl and 5 mM imidazole for Ni purification. The cell pellets were resuspended in the same buffer, and lysed by sonication. After centrifugation, the target proteins in the supernatants were purified. His-tagged proteins were purified by the Profinity IMAC Ni-Charged Resin (Bio-Rad, Hercules, Calif., USA). The amount of protein purified was quantified by absorbance at 280 nm and used for the relative expression yield calculations in Table 1.

Heat Stability The E. coli BL21 (DE3) strain harboring a protein expression plasmid (pET28a) was incubated in a 1-L Erlenmeyer flask with 100 mL of ZYM-5052 media containing 50 mg L⁻¹ kanamycin. Cells were grown at 37° C. with rotary shaking at 220 rpm for 16-24 hours. The cells were harvested by centrifugation at 12° C. and washed once with either 20 mM HEPES (pH 7.5) containing 50 mM NaCl and 5 mM MgCl₂. The cell pellets were re-suspended in the same buffer and lysed by sonication. After centrifugation, the target proteins in the supernatants were tested for heat stability at 50-80° C. for 30 minutes. The stability of the recombinant proteins was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and recorded by visual inspection, as described in Table 1.

TABLE 1
		Relative
A6PE UniProt ID	Heat Stability	Expression Yield
D9TQJ4	Untested due to low yields	20.6%
A0A090IXZ8	Untested due to low yields	27.8%
P32719	Untested due to mesophilic nature	54.6%
A8UV28	Untested due to lack of activity	86.5%
UPI000411882A	90% soluble after 30 minutes	81.6%
	at 60° C.
G7M2I3	60% soluble after 30 minutes	93.6%
	at 50° C.
A0A094WLM1	50% soluble after 30 minutes	134%
	at 50° C.
A0A223HZI7	80% soluble after 30 minutes	100%
	at 60° C.

Example 1. Assessing relative activity for the allulose 6-phosphate epimerase (A6PE)-dependent conversion of G1P to allulose in an improved process. The conversion of G1P to allulose by an enzymatic process including an A6PE with an amino acid sequence of UniProt ID A0A223HZI7 (“the A0A223HZI7 A6PE”) was compared to G1P to allulose conversion processes, which differed only with respect to the A6PE used in each process. More particularly, the G1P to allulose conversion was compared using processes, which included: a PGM with the amino acid sequence of UniProt ID A0A150LLZ1; a PGI with an amino acid sequence of UniProt ID Q5SLL6; the A0A223HZI7 A6PE or an A6PE with the amino acid sequence of either UniProt ID D9TQJ4, UniProt ID A0A090IXZ8, UniProt ID A8UV28, UniProt ID G7M213, UniProt ID A0A094WLM1, Uniparc ID UPI000411882A, or Uniprot P32719 (the P32719 enzyme is unstable at 50° C.); and an A6PP with an amino acid sequence of Uniprot ID A0A0E3NCH4. Each process was performed in 0.20 mL reaction mixturesaaa containing 38.5 mM G1P, 50 mM HEPES pH 7.2, 15 mM MgCl₂, 0.5 mM CoCl₂, 0.05 g/L PGM, 0.05 g/L PGI, 0.025 g/L A6PE, and 0.15 g/L A6PP. The reactions were incubated at 50° C. for 3 hours. A6PE was the rate limiting enzyme in the conversion of G1P to allulose. The reactions were stopped via enzyme filtration using a Vivaspin® 2 concentrator (10,000 MWCO), and analyzed by HPLC (Agilent 1100 series) using an Agilent Hi-Plex H column and a refractive index detector. The sample runs were in 5 mM H₂SO₄ at 0.6 mL/min for 15.5 minutes at 65° C.

Results showed no significant A6PE-dependent differences in activity, with the exception that the A6PE with the UniProt A8UV28 amino acid sequence was not active under the conditions tested.

Example 2. Assessing lower allulose 6-phosphate epimerase (A6PE)-dependent allulose to fructose conversion activity. The conversion of allulose to fructose by an enzymatic process including the A0A223HZI7 A6PE was compared to allulose to fructose conversion processes which differed only with respect to the A6PE used in each process. More specifically, the allulose to fructose conversion was compared using processes which included the A0A223HZI7 A6PE or an A6PE with the amino acid sequence of either UniProt ID D9TQJ4, UniProt ID A0A090IXZ8, UniProt ID G7M213, UniProt ID A0A094WLM1, UniProt ID A0A223HZI7, or UniParc ID UPI000411882A (the A6PEs with amino acid sequences of UniProt ID P32719 and UniProt ID A8UV28 were omitted due to incompatibility with the pathway). Each process was performed in 0.20 mL reaction mixtures containing 200 g/L allulose, 10 mM HEPES pH 7.2, 5 mM MgCl₂, 0.5 mM CoCl₂, and 0.025 g/L or 0.25 g/L A6PE. The reactions were incubated at 50° C. for 6 hours. The reactions were stopped via filtration of enzyme with a Vivaspin 2 concentrator (10,000 MWCO) and analyzed via HPLC (Agilent 1100 series) using a SupelCogel Pb-column and refractive index detector. The sample runs were in ultrapure water at 0.6 mL/min for 40 minutes at 80° C.

Results, summarized in Table 2, indicated the tested A6PEs produced relatively little fructose from allulose with the exception of enzymes with the amino acid sequences of UniProt ID A0A090IXZ8 and UniParc ID UPI000411882A. Notably, no conversion of allulose to fructose was observed for the A0A223HZI7 A6PE at an enzyme composition of 0.025 g/L

TABLE 2
	Conversion to fructose	Conversion to fructose
A6PE UniProt ID	at 0.025 g/L	at 0.25 g/L
D9TQJ4	0.1%	0.3%
A0A090IXZ8	1.2%	44.2%
P32719	Untested due to mesophilic nature
A8UV28	Untested due to lack of activity
UPI000411882A	0.6%	6.7%
G7M2I3	0.1%	1.0%
A0A094WLM1	0.1%	2.1%
A0A223HZI7	0%	1.0%

Example 3. Assessing relative activity of an allulose 6-phosphate epimerase (A6PE) with improved properties in the conversion of maltodextrin to allulose. The full-cascade conversion of maltodextrin to allulose by an enzymatic process including the A0A223HZI7 A6PE (which demonstrated no fructose-from-allulose activity) was compared to maltodextrin to allulose conversion processes, which differed only with respect to the A6PE used in each process, to determine how F6PEs with differing fructose-from-allulose activities affect allulose yield. More specifically, the maltodextrin to allulose conversion was compared using processes which included: an αGP with an amino acid sequence of UniProt ID G8NCC0; a PGM with an amino acid sequence of UniProt ID A0A150LLZ1; a PGI with an amino acid sequence of UniProt ID Q5SLL6; the A0A223HZI7 A6PE or an A6PE with an amino acid sequence of either UniProt ID A0A090IXZ8 (which demonstrated high fructose-from-allulose activity) or UniParc ID UPI000411882A (which demonstrated moderate fructose-from-allulose activity); an A6PP with an amino acid sequence of UniProt ID A0A0E3NCH4; and a 4GT with an amino acid sequence of UniProt ID E8MXP8. Each process was performed in 0.20 mL reaction mixtures containing 100 g/L debranched Sigma Aldrich maltodextrin DE 4-7, 25 mM sodium phosphate pH 7.2, 15 mM MgCl₂, 0.5 mM CoCl₂, 0.3 g/L αGP, 0.075 g/L PGM, 0.075 g/L PGI, 0.1 g/L A6PE, 0.1 g/L A6PP, and 0.04 g/L 4GT. The reactions were incubated at 50° C. for 18 hours such that the reaction was not fully complete at the time of analysis. The reaction were stopped via filtration of enzyme with a Vivaspin® 2 concentrator (10,000 MWCO) and analyzed via HPLC (Agilent® 1100 series) using a SupelCogel® Pb-column and refractive index detector. The sample runs were in ultrapure water at 0.6 mL/min for 40 minutes at 80° C.

Results, illustrated in FIG. 6, showed that the process involving the A6PE with the amino acid sequence of UniParc ID UPI000411882A produced substantially more fructose than that involving the A0A223HZI7 A6PE. As expected, the process involving the A6PE with the amino acid sequence of UniProt ID A0A090IXZ8 produced an intermediary amount of fructose. The process involving the A0A223HZI7 A6PE produced the most allulose in 18 hours. This resulted in the highest allulose yield pathway, and one more efficient than any previously disclosed for producing allulose using an A6PE. The relative affinities for F6P/A6P versus allulose for a given A6PE enzyme is demonstrated by the observed differences between fructose-from-allulose activity versus allulose-from-maltodextrin cascade. For example, while the A6PE with the amino acid sequence of UniProt ID A0A090IXZ8 produced mucher higher amounts of fructose when from allulose alone compared to the A6PE with the amino acid sequence of Uniparc ID UPI000411882A, in a full cascade reaction the A6PE with the amino acid sequence of Uniprot ID A0A090IXZ8 performs better since F6P/A6P are able to out compete allulose more efficiently for this enzyme than for the A6PE with the amino acid sequence of Uniparc ID UPI000411882A.

Example 4. Assessing relative activity of an allulose 6-phosphate phosphatase (A6PP) with improved properties in the conversion of G1P to allulose. The conversion of G1P to allulose by an enzymatic process using an A6PP with the amino acid sequence of UniProt ID A0A0E3NCH4 (“the A0A0E3NCH4 A6PP”) was compared to G1P to allulose conversion processes which differed only with respect to the A6PP used in each process. More specifically, the G1P to allulose conversion was compared using processes which included: a PGM with the amino acid sequence of UniProt ID A0A150LLZ1; a PGI with the amino acid sequence of UniProt ID Q5SLL6; an A6PE with the amino acid sequence of UniProt ID D9TQJ4; and either the the A0A0E3NCH4 A6PP or an A6PP with the amino acid sequence of UniProt ID A3DC21. The previously disclosed A6PPs with amino acid sequences of either Uniprot ID Q5LGR4 or Uniprot ID Q89ZR1 could not be included in the comparison because these enzymes are unstable at 50° C. Each process was performed in 0.20 mL reaction mixtures containing 38.5 mM G1P, 50 mM HEPES pH 7.2, 0.5 mM CoCl₂, 0.05 g/L PGM, 0.05 g/L PGI, 0.025 g/L A6PE, and 0.05 g/L A6PP. The reactions were incubated at 50° C. for 3 hours. A6PP was the rate limiting enzyme in the conversion of G1P to allulose. The reactions were stopped via filtration of enzymes using a Vivaspin® 2 concentrator (10,000 MWCO) and analyzed via HPLC (Agilent 1100 series), using an Agilent Hi-Plex® H-column and refractive index detector. The samples runs were in 5 mM H₂SO₄ at 0.6 mL/min for 15.5 minutes at 65° C. Results, summarized in Table 3, showed a 2.2-fold improvement in allulose production using the A0A0E3NCH4 A6PP relative to the process using the previously disclosed A6PP with the amino acid sequence of UniProt ID A3DC21.

TABLE 3
                Relative activity
A6PP Uniprot ID at 50° C. (%)
A3DC21          100
Q5LGR4          N/A
Q89ZR1          N/A
A0A0E3NCH4      220

SEQUENCE LISTING
A6PE;
UniProt ID A0A223HZI7;
SEQ ID NO: 1
Thermoanaerobacterium thermosaccharolyticum
MKPMFAPSLMCANFLDLKNQIEILNERADIYHIDI
MDGHYVKNFALSPYLMEQLKTIAKIPMDAHLMVEN
PADFLECIAKSGATYISPHAETINKDAFRIMRTIK
ALGCKTGIVLNPATPVEYIKYYIGMLDKITILTVD
AGFAGQTFINEMLDKIAEIKSLRDQNGYSYLIEVD
GSCNEKTFKQLAEAGTDVFVVGSSGLFNLDTDLKV
AWDKMMDTFTRCTSN;
A6PP;
UniProt ID A0A0E3NCH4;
Methanosarcina thermophila
SEQ ID NO: 2
MLKALIFDMDGVLVDSMPFHAAAWKKAFFEMGMEI
QDSDIFAIEGSNPRNGLPLLIRKARKEPEAFDFEA
ITSIYRQEFKRVFEPKAFEGMKECLEVLKKRFLLS
VVSGSDHVIVHSIINRLFPGIFDIVVTGDDIINSK
PHPDPFLKAVELLNVRREECVVIENAILGVEAAKN
ARIYCIGVPTYVEPSHLDKADLVVEDHRQLMQHLL
SLEPANGFRQ;
A6PE;
UniProt ID D9TQJ4;
Thermoanaerobacterium thermosaccharolyticum
SEQ ID NO: 3
MKYLFSPSLMCMNLIKLNEQISVLNSKADFLHVDI
MDGHFVKNITLSPFFIEQIKSYVNIPIDAHLMVEN
PGDYIEICEKSGASFITIHAETINREAFRIIDRIK
SHGLMVGIALNPATPISEIKHYINKIDKITIMTVD
PGFAGQPFIPEVLEKIRDLKRLKDDNNYNYLIEAD
GSCNKNTFQVLKDAGCKVFVLGSSGLFNLSDDLGK
AWEIMIGNFNG;
A6PE;
UniProt ID A0A090IXZ8;
Bacillus thermoamylovorans
SEQ ID NO: 4
MSNKIEFSPSLMTMDLDKFKEQITFLNNHVGSYHI
DIMDGHYVPNITLSPWFVQEVRKISDVPMSAHLMV
TNPSFWVQQLIDIKCEWICMHVETLDGLAFRLIDQ
IHDAGLKAGVVLNPETSVDAIRPYIDLVDKVTIMT
VDPGFAGQRFIDSTLEKIVELRKLREEHGYKYVIE
MDGSSNRKSFKKIYEAGPDIYIIGRSGLFGLHEDI
EKAWEIMCKDFEEMTGEKVL;
A6PE;
UniProt ID P32719;
Escherichia coli
SEQ ID NO: 5
MKISPSLMCMDLLKFKEQIEFIDSHADYFHIDIMD
GHFVPNLTLSPFFVSQVKKLATKPLDCHLMVTRPQ
DYIAQLARAGADFITLHPETINGQAFRLIDEIRRH
DMKVGLILNPETPVEAMKYYIHKADKITVMTVDPG
FAGQPFIPEMLDKLAELKAWREREGLEYEIEVDGS
CNQATYEKLMAAGADVFIVGTSGLFNHAENIDEAW
RIMTAQILAAKSEVQPHAKTA;
A6PE;
UniProt ID A8UV28;
Hydrogenivirga sp. 128-5-R1-1
SEQ ID NO: 6
MEKLLAPSILAGDWWNIGEQIEATLRGGADIIHFD
VMDGHFVPNITVGPEILTSISRRVNVPVDAHLMIE
NPDRYIPSFVEAGAKWISVHIENVPHIHRTLTLIR
ELGAKAGVVLNPGTPLSAVEEAIHYADYVLLMSVN
PGFSGQRFIERSLERLSLLRDMRDRLNPDCLIEVD
GGVKEDNVVEVVRAGADVVVVGSGIFSAKDVEAQT
RKLKDLISSAVAV;
A6PE;
UniParc ID UPI000411882A;
Brevibacillus thermoruber
SEQ ID NO: 7
MGFKFSPSLMCMNLLDIQHQIEVMNRRADLVHIDI
MDGHYVKNLTLSPFFIEQLKESLHVPMDVHLMVEN
PTDFIERVKEAGASIISPHAETINTDAFRIIDKVK
SLGCQMGIVLNPATPIAYIQHYIHLVDKITIMTVD
PGYAGQKFIPEMLEKIRQAKRLKEERGYRYLIEVD
GSCNVGTFKRLAEAGAEVFIVGSSGLFNLHPDLEV
AWDMMMDNFQREVGETTA;
A6PE; UniProt ID
G7M2I3;
Clostridium sp. DL-VIII
SEQ ID NO: 8
MKPMFAPSLMCANFLDLKNQIEILNERADIFHVDI
MDGHYVKNFSLSPAMMEQLKTITKIPMDAHLMVEN
PADFLEGIAKAGATYISPHAETINKDAFRIMRTIK
ALGCKTGVVLNPATPVEYIKHYLGMLDKITILTVD
AGFAGQTFIEEMLDKIEEVKRLREENGYSYLIEVD
GSCNEKTFKKLAEAGTEVFIVGSSGLFNLDADLKV
SWDKMMNMFNKCINN;
A6PE; UniProt ID
A0A094WLM1;
Bacillus alcalophilus
SEQ ID NO: 9
MYKFSPSLMCMDLSRFKEQVEVLNDKADFYHVDIM
DGHFVKNITLSPFFIQELKKITDVPIDAHLMVTNP
ADFVEMTIDAGADYISLHAETINGNAFRLINQIKE
KGKKFGVVLNPATPLESIRHYIQHVDKLTIMTVDP
GFAGQKFVEEMIGKIKEAKELKERNGYKYLITIDG
SCNKNTFKKLVEAGAEVLIVGSSGLFGLDEDVNIA
WDKMMDTFHLEVKDISQV;
A6PP; UniProt ID
A3DC21;
Hungatelclostridium thermocellum
SEQ ID NO: 10
MIKYKAVFFDFDYTLADSSKAVIECINYALQKMGY
PESSPESICRTIGLTLAEAFKILSGDTSDSNADLF
RQYFKERADLVMCDRTVMYSTVECVLKKLKKADVK
TGIVSTKYRYRIEDILKRDKLLQYFDVIVGGEDVA
AHKPDPEGLLKAISMVGCQKEEVLFVGDSTVDART
AKNAGVDFVAVLTGTTGANEFSEYNPGAVIEDLSG
LLDMFML;
A6PP; UniProt ID
Q5LGR4;
Bacteroides fragilis
SEQ ID NO: 11
MKYTVYLFDFDYTLADSSRGIVTCFRSVLERHGYT
GITDDMIKRTIGKTLEESFSILTGITDADQLESFR
QEYSKEADIYMNANTILFPDTLPTLTHLKKQGIRI
GIISTKYRFRILSFLRNHMPDDWFDIIIGGEDVTH
HKPDPEGLLLAIDRLKACPEEVLYIGDSTVDAGTA
AAAGVSFTGVTSGMTTAQEFQAYPYDRIISTLGQL
ISVPEDKSGCPL;
A6PP; UniProt ID Q89ZR1;
Bacteroides thetaiotaomicron
SEQ ID NO: 12
MNYKTYLFDFDYTLADSSRGIVTCFRNVLNRHQYT
NVTDEAIKRTIGKTLEESFSILTGVTDWEQLTAFR
QEYRLEADVHMNVNTRLFPDTLSTLKELKERGARI
GIISTKYRFRILSFLDEYLPENFLDIVVGGEDVQA
AKPSPEGIKFALEHLGRTPQETLYIGDSTVDAETA
QNAGVDFAGVLNGMTTADELRAYPHRFIMENLSGL
LYI;
PGM; UniProt ID AOA15OLLZ1;
Caldibacillus debilis
SEQ ID NO: 13
MEWKQRAERWLRFENLDPELKKQLEEMAKDEKKLE
DLFYKYLEFGTGGMRGEIGPGTNRINIYTVRKASE
GLARFLLASGGEEKAKQGVVIAYDSRRKSREFALE
TAKTVGKHGIKAYVFESLRPTPELSFAVRYLHAAA
GVVITASHNPPEYNGYKVYGEDGGQLTPKAADELI
RYVYEVEDELSLTVPGEQELIDRGLLQYIGENIDL
AYIEKLKTIQLNRDVILNGGKDLKIVFTPLHGTAG
QLVQTGLREFGFQNVYVVKEQEQPDPDFSTVKSPN
PEEHEAFEIAIRYGKKYDADLIMGTDPDSDRLGIV
VKNGQGDYVVLTGNQTGAILLYYLLSQKKEKGMLV
RNSAVLKTIVTSELGRAIASDFGVETIDTLTGFKF
IGEKIKEFKETGSHVFQFGYEESYGYLIGDFVRDK
DAIQAALFAAEAAAYYKAQGKSLYDVLMEIYKKYG
FYKESLRSITLKGKDGAEKIRAIMDAFRQNPPEEV
SGIPVAITEDYLTQKRVDKAAGQTTPIHLPKSNVL
KYYLADESWFCIRPSGTEPKCKFYFAVRGDSEAQS
EARLRQLETNVMAMVEKILQK;
PGI; UniProt ID Q5SLL6;
Thermus thermophilus
SEQ ID NO: 14
MLRLDTRFLPGFPEALSRHGPLLEEARRRLLAKRG
EPGSMLGWMDLPEDTETLREVRRYREANPWVEDFV
LIGIGGSALGPKALEAAFNESGVRFHYLDHVEPEP
ILRLLRTLDPRKTLVNAVSKSGSTAETLAGLAVFL
KWLKAHLGEDWRRHLVVTTDPKEGPLRAFAEREGL
KAFAIPKEVGGRFSALSPVGLLPLAFAGADLDALL
MGARKANETALAPLEESLPLKTALLLHLHRHLPVH
VFMVYSERLSHLPSWFVQLHDESLGKVDRQGQRVG
TTAVPALGPKDQHAQVQLFREGPLDKLLALVIPEA
PLEDVEIPEVEGLEAASYLFGKTLFQLLKAEAEAT
YEALAEAGQRVYALFLPEVSPYAVGWLMQHLMWQT
AFLGELWEVNAFDQPGVELGKVLTRKRLAG;
4GT; UniProt ID E8MXP8;
Anaerolinea thermophila
SEQ ID NO: 15
MSLFKRASGILLHPTSLPGPDGIGDLGPEAYRWVN
FLAESGCSLWQILPLGPTGFGDSPYQCFSAFAGNP
YLVSPALLLDEGLLTSEDLADRPEFPASRVDYGPV
IQWKLTLLDRAYVRFKRSTSQKRKAAFEAFKEEQR
AWLLDFSLFMAIKEAHGGASWDYWPEPLRKRDPEA
LNAFHRAHEVDVERHSFRQFLFFRQWQALRQYAHE
KGVQIIGDVPIFVAYDSADVWSHPDLFYLDETGKP
TVVAGVPPDYFSATGQLWGNPLYRWDYHRETGFAW
WLERLKATFAMVDIVRLDHFRGFAGYWEVPYGMPT
AEKGRWVPGPGIALFEAIRNALGGLPIIAEDLGEI
TPDVIELREQLGLPGMKIFQFAFASDADDPFLPHN
YVQNCVAYTGTHDNDTAIGWYNSAPEKERDFVRRY
LARSGEDIAWDMIRAVWSSVAMFAIAPLQDFLKLG
PEARMNYPGRPAGNWGWRYEAFMLDDGLKNRIKEI
NYLYGRLPEHMKPPKVVKKWT;
αGP; UniProt ID G8NCC0;
Thermus sp. CCB_US3_UF1
SEQ ID NO: 16
MPLLPEPLSGLKELAYNLWWSWNPEAAELFQEIDP
SLWKRFRGNPVKLLLEADPGRLEGLAATSYPARVG
AVVEALRAYLREREEKQGPLVAYFSAEYGFHSSLP
IYSGGLGVLAGDHVKAASDLGLNLVGVGIFYHEGY
FHQRLSPEGVQVEVYETLHPEELPLYPVQDREGRP
LRVGVEFPGRTLWLSAYRVQVGAVPVYLLTANLPE
NTPEDRAITARLYAPGLEMRIQQELVLGLGGVRLL
RALGLAPEVFHMNEGHSAFLGLERVRELVAEGHPF
PVALELARAGALFTTHTPVPAGHDAFPLELVERYL
GGFWERMGTDRETFLSLGLEEKPWGKVFSMSNLAL
RTSAQANGVSRLHGEVSREMFHHLWPGFLREEVPI
GHVTNGVHTWTFLHPRLRRHYAEVFGPEWRKRPED
PETWKVEALGEEFWQIHKDLRAELVREVRTRLYEQ
RRRNGESPSRLREAEKVLDPEALTIGFARRFATYK
RAVLLFKDPERLRRLLHGHYPIQFVFAGKAHPKDE
PGKAYLQELFAKIREYGLEDRMVVLEDYDMYLARV
LVHGSDVWLNTPRRPMEASGTSGMKAALNGALNLS
VLDGWWAEAYNGKNGFAIGDERVYESEEAQDMADA
QALYDVLEFEVLPLFYAKGPEGYSSGWLSMVHESL
RTVGPRYSAARMVGDYLEIYRRGGAWAEAARAGQE
ALAAFHQALPALQGVTLRAQVPGDLTLNGVPMRVR
AFLEGEVPEALRPFLEVQLVVRRSSGHLEVVPMRP
GPDGYEVAYRPSRPGSYAYGVRLALRHPITGHVAW
VRWA;

Claims

1. An improved process for the production of allulose from a saccharide, the improvement comprising converting fructose-6-phosphate (F6P) to allulose 6-phopsphate (A6P) using an allulose 6-phosphate epimerase (A6PE), wherein the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1.

2. An improved process for the production of allulose from a saccharide, the improvement comprising converting A6P to allulose using an allulose-6-phosphate phosphatase (A6PP), wherein the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2.

3. The process of claim 2, further comprising a step of converting fructose-6-phosphate (F6P) to allulose 6-phopsphate (A6P) using an allulose 6-phosphate epimerase (A6PE) wherein the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1.

4. The process of any one of claims 1-3, further comprising a step of converting glucose 6-phosphate (G6P) to the F6P, wherein the step is catalyzed by a phosphoglucose isomerase (PGI).

5. The process of claim 4, further comprising the step of converting glucose 1-phosphate (G1P) to the G6P, wherein the step is catalyzed by a phosphoglucomutase (PGM).

6. The process of claim 5, further comprising the step of converting a saccharide to the G1P, wherein the step is catalyzed by at least one enzyme, wherein the saccharide is selected from the group consisting of a starch or derivative thereof, cellulose or a derivative thereof and sucrose.

7. The process of claim 6, wherein the at least one enzyme is selected from the group consisting of alpha-glucan phosphorylase (αGP), maltose phosphorylase, sucrose phosphorylase, cellodextrin phosphorylase, cellobiose phosphorylase, and cellulose phosphorylase.

8. The process of claim 6, wherein the saccharide is starch or a derivative thereof selected from the group consisting of amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltose, maltotriose, and glucose.

9. The process of claim 8, further comprising the step of converting starch to a starch derivative wherein the starch derivative is prepared by enzymatic hydrolysis of starch or by acid hydrolysis of starch.

10. The process of claim 9, wherein a 4-glucan transferase (4GT) is added to the process.

11. The process of claim 9, wherein the starch derivative is prepared by enzymatic hydrolysis of starch catalyzed by an isoamylase, a pullulanase, an alpha-amylase, or a combination thereof.

12. The process of any one of claims 1-3, further comprising:

a step of converting fructose to F6P catalyzed by at least one enzyme; and

optionally, a step of converting sucrose to fructose catalyzed by at least one enzyme.

13. The process of claim 4, further comprising:

a step of converting glucose to G6P catalyzed by at least one enzyme, and

optionally, a step of converting sucrose to glucose catalyzed by at least one enzyme.

14. The process of claim 2, wherein the process is an enzymatic process to produce allulose comprising the steps of: wherein process steps (i)-(v) are conducted in a single reaction vessel.

(i) converting a saccharide to glucose 1-phosphate (GIP) using an α-glucan phosphorylase or starch phosphorylase, wherein the saccharide is selected from the group consisting of starch, one or more derivatives of starch, or a combination thereof;

(ii) converting GIP to glucose 6-phosphate (G6P) using a phosphoglucomutase (PGM);

(iii) converting G6P to fructose 6-phosphate (F6P) using a phosphoglucoisomerase (PGI);

(iv) converting the F6P to allulose 6-phopsphate (A6P) using an allulose 6-phosphate epimerase (A6PE), and

(v) converting the A6P to allulose using an allulose 6-phosphate phosphatase (A6PP), wherein the A6PP comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 2,

15. The process of claim 14, wherein the A6PE comprises an amino acid sequence having at least 90% sequence identity to SEQ ID NO: 1.

16. The process of claim 14 or 15, wherein the process steps are conducted under at least one of the following process conditions:

(a) at a temperature ranging from about 37° C. to about 85′C;

(b) at a pH ranging from about 5.0 to about 9.0; or

(c) for about 1 hour to about 48 hours.

17. The process of any one of claim 14-16, wherein the process steps are conducted under at least one of the following process conditions:

(a) without adenosine triphosphate (ATP) as a source of phosphate;

(b) without nicotinamide adenosine dinucleotide;

(c) at a phosphate concentration from about 0.1 mM to about 150 mM;

(d) at a Mg2+ concentration from about 0.1 mM to 50 mM;

(e) at a Co2+ concentration from about 0.1 mM to 50 mM;

(f) wherein phosphate is recycled; and

(g) wherein at least one step of the process involves an energetically favorable chemical reaction.

18. The process of claim 17, wherein phosphate is recycled, and wherein phosphate ions produced by A6PP dephosphorylation of A6P are used in the process step of converting a saccharide to G1P.

19. The process of claim 17, wherein the step of converting A6P to allulose is an energetically favorable, irreversible reaction.

20. The process of any one of claims 14-19, further comprising the step of separating recovering the allulose produced, wherein the separation recovery is not via chromatography separation.

21. The process of claim 14 or 15, wherein the derivatives of starch are selected from the group consisting of amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltotriose, maltose, and glucose.

22. Allulose produced from a process of any one of claims 1-21.

23. A consumable product containing allulose produced from a process of any one of claims 1-21.